Galectins are a family of beta-galactoside-binding proteins. The expression of galectins in macrophages, eosinophils and basophils suggests that galectins play roles in innate immunity. Galectin interactions with T and B lymphocytes further suggests that galectins also play important roles in adaptive immunity. Because of its external fertilization and development, transparent embryos, short generation time, powerful genetic systems, and extensive genomic resources, the zebrafish (Danio rerio) is a useful model system for in vivo studies of immunology. We will therefore use the zebrafish to gain insight into the biological functions of galectins in innate and adaptive immunity. Galectins have been shown to interact with several types of viruses. Rhabdoviruses and birnaviruses that infect zebrafish have glycosylated proteins on their virion exterior that may interact with galectins. Such interactions may affect characteristics of both the viral replication cycle and the host anti-viral immune response. We hypothesize that zebrafish galectins are involved in host defense by interacting directly or indirectly with potential viral pathogens. Moreover, manipulation of zebrafish galectins will alter the pathogenicity of and host immune responses to viral agents. We will first characterize direct and indirect interactions between zebrafish galectins and viruses in vitro by identifying the carbohydrates present on viral glycoproteins, assaying for direct and indirect galectin-virus interactions by affinity chromatography and plaque assay on zebrafish cells in culture, respectively. Effects of galectins on viral replication will be monitored. We will then assess the effects of viral challenge on galectins in zebrafish cell lines, monitoring galectin expression levels and intracellular localization as well as the induction of cytokine expression in infected cultures. This will include assaying the activation of gene promoters harboring elements responsive to anti-viral IFNg stimulation. Finally, we will assess the effects of galectin-virus interactions on innate and adaptive immune responses in vivo, employing both morpholino- modified antisense oligonucleotides and transgenesis to create knockdown models of galectin expression. Zebrafish survival, viral replication kinetics, and the tissue distribution and expression levels of galectins, cytokines, and immune cells will be monitored. Significant evidence suggests that galectins participate in both innate and adaptive immunity, and that they interact with viral pathogens. Information obtained through the proposed studies in the zebrafish model will be applicable to higher vertebrates, and will elucidate the roles galectins play in immunity as well as the mechanisms by which galectin-virus interactions act to modulate immune functions.